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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

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i8o

IRON

c.c. of hydrochloric acid (D ~- 1-19). When the action slackens, the flask
is heated carefully on a water-bath until the smell of chlorine, disappears
and, when cold, 200 c.c. of hydrochloric acid (I) 1-19) and 50 grams of
ferrous chloride or, better, 25-30 grains of cuprous chloride, free from arsenic,
are added.

To the neck of the distilling ilask is (Hied, by means of two grey rubber
stoppers, an internal pressure regulator, consisting of a.n inverted flask
rather less than half filled with concentrated hydrochloric acid and fitted

with tubes / and I1 of about 6
mm. bore (sec. Fig. 14) which, if
the pressure falls, allow air to
enter the Ilask and rapidly to re-
establish the equilibrium. The
eoneentnited hydrochloric acid in
the regulating Ilask, as it gradu-
ally becomes heated, further tends
to increase the pressure and thus
contributes to the regularity of
,          the distillation.

The side-tube of the distill-
ing Ilask provided with a, small
bulb to prevent drops spurted
from the boiling liquid from ris-
ing along the side-tube is then
connected with a looe.e. pipette,
which dips for a few millimetres
into boiled water rendered alka-
line with 50 f)o c.c. of ammonia
(1) o-yi) and mixed with a few
drops of methyl orange, this being
contained in a moderately large
beaker si a tiding in a, bath of cold
"""""""" water. The flask is then heated
and most of the liquid contained
in it slowly distilled until the solution in the beaker, becoming acid,
assumes a faintly red colour.

At this point the pipette is removed and rinsed out with a little water,
the, distillate being rendered alkaline by a slight excess of powdered sodium
bicarbonate, mixed with a, little starch paste and titrated with the iodine
solution ; the proportion of arsenic in the metal is thus ascertained.

***

Cast-irons always con tain marked qnant.il ies of impurities ; they are brittle!
and non-inalk'abkt.

(irey cttsl-irnits arc more or less dark in colour according to their content
in graphitic carbon, and they have a granular structure, melt at; about uoo°
ami have, the specific gravity 7-0 7-2. They contain considerable proportions
of silicon (from i% in the paler products to 3 5% in 11 u; darker ones, the mean from a burette until the liquid